Green roof issue (u-value and material problems)

Hi Mostapha, Chris and group members,

There are two questions about the Green roof issue as I ran the gh file named "Green Roof In Energy Model" . I'll appreciate it if you give me a hand.

A. Can’t run correctly within Honeybee_Export To OpenStudio as opposite to the Honeybee_Run Energy Simulation. After I uploaded the Green roof construction setting into honeybee library, it still can't work. The error said:

1. Honeybee currently can't calculate U-Values for Material:RoofVegetation.

Your Honeybee EnergyPlus simulations will still run fine with this material and this is only a Honeybee interface limitation..

Let us know if you think HB should calcualte this material type and we will add it to the list. :)

2. The material type Material:RoofVegetation hasn't been implemented yet!

 Solution exception:openstudio::model::Material const & type is null

So how could I manage to calculate the influence by green roof in openstudio component as I also tend to calculate Light Control in openstudio component? 

B. I used Honeybee_Decompose EP Construction to check the Green Roof construction's U-value_SI, it is -1.133198. Why it could be negative, what does it mean when u-value is negative?

Thank you in advance. 

Xiaojian